John Meacham wrote:
On Fri, Jan 27, 2006 at 12:28:23PM +1100, Donald Bruce Stewart wrote:
john:
I have often wanted a shorthand syntax for testing if a value
matches a given pattern. I want to implement such an extension for
jhc but can't decide an appropriate syntax so I thought I'd ask the
group. basically I want something like
/Left (Just _)/ expands to
\x -> case x of
Left (Just _) -> True
_ -> False
Something like pattern guards?
f x | Just _ <- x = putStrLn "something"
hmm.. how about
(| Left (Just _) |)
since | cannot be used as a section so it can be unambigously lexed
as a different symbol. I think I like it. any other ideas?
John
(@ Left (Just _) @) would fit in with the use of @ in as-patterns
Also, the as-pattern syntax could be stolen for expressions so that [EMAIL PROTECTED]
would evaluate to True or False when this syntactic form appears in an
expression instead of a pattern ie to give the following equivalence:
(@ pat @) exp === exp @ pat
Regards, Brian.
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